1. Technical Field
The present invention relates to a liquid ejecting apparatus and a head unit including a head which is provided in the liquid ejecting apparatus.
2. Related Art
As a liquid ejecting apparatus such as an ink jet printer, there is a known apparatus which adopts a piezoelectric element as an actuator to eject ink droplets. In order to drive the piezoelectric element, it is necessary to apply a drive signal having amplitude of several tens of volts at the peak value. In the related art, an analog amplification circuit having a bipolar transistor subjected to a push-pull connection is mounted on a drive substrate which generates the drive signal. However, there has been a disadvantage in that a heat sink for dissipating heat is necessary on account of unfavorable efficiency of power conversion and a large calorific value.
The inventors, taking the above-described problem into consideration, have proposed to use a digital amplification circuit having more excellent efficiency of power conversion than that of the analog amplification circuit (for example, JP-A-2011-5733). The digital amplification circuit adopts a pulse modulation technology, thereby having more excellent efficiency of power conversion than that of the analog amplification circuit and making it possible to suppress heat generation.
However, there is a disadvantage in that heat generation of a level which is not negligible occurs even though a digital amplification circuit is adopted. The digital amplification circuit is generally configured to have a switching element and a coil (a low-pass filter), but when there is a need to supply electrical charges to a large number of piezoelectric elements such as the low-pass filters and to apply voltages to eject liquid droplets by driving the piezoelectric element, the coil receives an extremely large load. The heat generation of a coil particularly becomes a major disadvantage in a line printer and the like having a large number of nozzles.
The heat generation of a coil causes the resistance value and the inductance of the coil to change, thereby resulting in changes of characteristics of a signal which is restored through the coil. When the characteristics of the signal change, an operation of a piezoelectric element which has been driven based on the signal changes in response to a temperature change of the coil. Thus, a pressure change of a cavity which has changed by the operation of the piezoelectric element also changes. Eventually, there are possibilities that the amount of liquid droplets ejected from nozzles may change, images printed on a medium may change, and deterioration of image quality may be caused. There is another possibility that when the temperature is excessively high, long-term quality of components (for example, a capacitor) which are arranged together with the coil may be influenced.